Respiratory Syncytial Virus (RSV) is a common cold virus belonging to the family of paramyxovirus. RSV is virulent, easily transmissible and the most common cause of lower respiratory tract disease in children of less than 2 years of age. Up to 98% of children attending day care will be infected in a single RSV season. Between 0.5% and 3.2% of children with RSV infection require hospitalization. Approximately 90,000 hospital admissions and 4500 deaths per year were reported in United States. Major risk factors for hospitalization due to RSV are premature birth, chronic lung disease, congenital heart disease, compromised immunity, and age younger than 6 weeks in otherwise healthy children.
Two subtypes of RSV have been identified, subtype A and subtype B. RSV has two major surface glycoproteins, the fusion protein (F protein) and the attachment protein (G protein). The F protein of RSV is a viral membrane protein and responsible for fusion of the virion with a host cell after attachment. In addition, infection of neighboring cells through the formation of syncytia is promoted by the F protein and its function is thought to depend on the original oligomeric structure of the protein. The G protein is a 89 kD protein, which is also known as the attachment protein. The G protein differs considerably between the two RSV subtypes, whereas the F protein is more conserved. Approximately 53% homology is present within a G protein from subtypes A and B. Although G protein is not required for infection of host cells, anti-RSV G antibodies have shown to improve symptoms in animal models and can induce virus neutralization in the presence of complement.
Antibodies against the F or G protein of RSV have been described. Palivizumab is a genetically engineered, humanized monoclonal antibody against the F protein. WO 2008/147196 discloses sequences of human RSV F protein binding molecules. A mouse monoclonal antibody (131-2G) against the G protein has been described, which is thought to bind to a CX3C (fractalkine) motif in the RSV G protein, which motif is capable of binding to the CX3CR1 (Fractalkine) receptor on NK cells, T cells and monocytes. This antibody was demonstrated to reduce migration of PBMCs towards RSV G glycoprotein (Tripp et al., 2001, Nat. Immunol. 2001, 2(8):732-8). Antibody 131-2G does not neutralize RSV in vitro, however, in an in vivo mouse model dosing at 300 mg/mouse resulted in reduced RSV A2 recovery from lungs, reduced pulmonary inflammation, and lowered IFN-gamma levels in a mouse model. Human monoclonal antibodies against RSV G protein have been described in U.S. 2010-0285022, WO 2009/055711 and Collarini et al. (Journal of Immunology, 2009, 183: 6338-6345). The antibodies bind to a conserved epitope in the G protein close to the CX3C domain, which is located in a region of the G protein corresponding to amino acid positions 164-172.
No effective treatment of RSV positive bronchiolitis beside supportive care in the form of adequate nutrition and oxygen therapy is currently available. Antiviral therapies such as Ribavirin have not been proven to be effective in RSV infection. Only monoclonal antibody palivizumab (also called Synagis), is registered for prophylaxis against RSV infection. However, palivizumab is not always effective. It is only useful and approved for prophylactic treatment of premature infants up to 4 KG body weight. Thus, palivizumab cannot be used to treat an established RSV infection. Furthermore, palivizumab is only partly effective as it reduces hospitalization of infants by approximately 50%.
Therefore, there is a need for additional antibodies and therapies against RSV.